The present invention relates to sealing glass composition and an electrically conductive mixture of said composition. More particularly, the invention relates to a sealing glass composition for bonding semiconductor chips, also known as "dies", to ceramic substrates and, still more particularly, to a composition useful in bonding such dies to ceramic substrates by firing at temperatures less than 400.degree. C. According to one aspect of the invention, the sealing glass composition is formulated in an electrically conductive paste, such as a silver paste, which is particularly effective to bond silicon semi-conductive devices to ceramic substrates.
It has been known to employ silver-filled glass to bond semi-conductor devices to ceramic substrates which may or may not be metalized. Such pastes are, for example, described in Dietz, et al., U.S. Pat. Nos. 4,401,767, Dietz, et al., U.S. Pat. No. 4,436,785, Dietz, et al., U.S. Pat. No. 4,459,166, Husson, Jr. et al., U.S. Pat. No. 4,636,254 and Husson, Jr. et al., U.S. Pat. No. 4,761,224.
Although the silver paste compositions heretofore known have broad utility in the semi-conductor industry, a problem arises in the use of such compositions in conjunction with semi-conductor devices that cannot withstand the elevated temperature to which the devices may be exposed during bonding of the semi-conductor devices to ceramic substrates. Until now sealing glass compositions and silver paste formulations which have been used required heating at temperatures in excess of 400.degree. C., e.g. 430.degree. C., to effect both satisfactory bonding and development of adequate bonding strength. For example, sealing glasses based on lead borate systems such as been commonly used require firing at 430.degree. C. to produce the desired bond strength. However, many of the new semi-conductor dies are much more sensitive to firing temperature than previous devices and their usefulness is adversely effected by exposure to such temperatures. Dies which are sensitive to elevated firing temperatures include larger dies and dies employing fine line geometry. In the latter case, lines of Si-Si02-Si are spaced 1 to 2 microns apart are provided at the die surface. Firing at high temperature to accomplish satisfactory bonding tends to destroy the usefulness of these dies due to incipient melting of the line compositions which may result in undesirable contact between the lines.
It is therefore desirable to be able to provide a sealing glass composition and silver paste made therefrom which does not require firing at these elevated temperatures to achieve satisfactory bond strength.